At present, conventional units of thermal power and hydropower have reliable power generating capacity and good power regulating capacity. Thus, during inspection and maintenance, the effect of these units have on the power gird is mainly shown in the aspect of the reliability of power supply. While arranging maintenance of conventional units, it is usually necessary to consider and guarantee the reliability of power supply of the grid. The corresponding methods include equal reserve, equal risk degree, etc. Compared with conventional units of thermal power and hydropower, wind turbine power generating unit is special. Thus, the effect of wind turbine power generating unit has on the power grid is different from the effect of conventional generator units have on the grid.
A wind power plant is generally characterized in that it has many wind turbines, each single turbine has a small capacity and wind farms are geographically widely spread. Limited by maintenance manpower and material resources, the entire wind power plant cannot be stopped during maintenance of the wind power plant. Usually, maintenance is conducted in batches according to geographical distribution of wind turbines. With this maintenance method, the number of the turbines arranged to be maintained is limited in number for each time and as capacity of a single wind turbine is small, its controllability is bad and confidence level of its capacity is not very high. As it is shown in operating conditions of Gansu Wind Farm in 2011, wind power output of the entire grid mainly concentrates on the installed capacity output of 5%˜35%, frequency of occurrence is 43%. The temporal frequency for installed capacity of 0%˜5% is 30% and temporal frequency for installed capacity of over 65% is 6%. It can be seen that capacity replacement benefit of wind turbines is limited during maintenance of each time and its influence on reliability of grid power supply is not as serious as conventional thermoelectric units and hydroelectric generating units. Therefore, when one makes maintenance schedule for a wind power plant, the effect on reliability of electric power system takes a second place.
As wind power is a green and renewable energy source. One of its vital functions in power grid is replacing conventional fossil energy to generate electricity in order to reduce emission of greenhouse gases and harmful gases, so as to reduce the consumption of conventional fossil energy and improve energy saving and emission reduction of the power grid. Economically, wind power plant maintenance mainly affects its energy saving and emission reduction. As generation of electrical energy at wind power plant varies in seasons, it needs to focus on how to reduce wind curtailment quantity of wind power plant maintenance while formulating maintenance schedule, so as to take full advantage of wind power resources, which have the benefits of energy saving and emission reduction of the power grid.
Formulating maintenance schedule for generating units is not only important for operation and dispatching of electric power system, but also important for long-term planning of electric power system. Formulating maintenance schedule for generating units is to make preventative maintenance on generating units to keep them in good technical conditions, reduce failure, prolong their service life and improve reliability of the overall electric power system.
The planned maintenance items for wind power plant generally include: lubricating, tightening screws, replacing filters, checking safeguard measures, etc. At present, most of foreign wind power plants adopt planned maintenance. For example, Sweden Vattenfall generally makes planned maintenance on its wind power plants once every two years, which is divided into overhaul and line check as overhaul needs about two maintenance workers to work for seven labor hours and line check needs about two maintenance workers to work for four labor hours; Denmark Elsam electric power company makes maintenance on small and old wind turbines once every 3˜6 months and the maintenance on large and new wind turbines will be made every half to one year, as it takes about two maintenance workers to work about fifteen hours for each wind turbine.
Wind power plant maintenance is an important part in operating maintenance of wind power plant and compared with conventional power supplies like thermal power and hydropower, wind power plant is of the characteristics like wind power plants are widely distributed geographically, units are large in number, natural environmental is complex and changeable and seasonal variation of wind power output is large, which make the wind power plant cannot ensure generating efficiency during maintenance.